The long-term objective of this project is to develop a rapid, inexpensive and reliable assay to monitor the presence of praziquantel (PZQ) resistant schistosomes in humans. The proposal is a response to recent studies that suggest resistance to PZQ may exist in some parts of Africa, including Egypt, where the PI and colleagues have shown that some villagers infected by schistosomes cannot be cured by 3 doses of the drug. The proposal includes 4 specific aims that are somewhat interdependent: First, they propose to characterize the biological properties of schistosomes that are less susceptible to PZQ both in vivo and in vitro. Second, they will attempt to determine if the apparent resistance to PZQ is genetically transmitted. Third, they will attempt to identify the gene(s) that underlie or are linked to PZQ resistance, and use this information to develop a convenient assay that is capable of detecting resistant isolates using miracidia obtained from eggs shed by infected individuals. Fourth, once this assay is developed, they will examine its utility under field conditions. The proposal states that results obtained from this study, and subsequent epidemiological studies using the assay(s) that evolve from it, will be used to assess the emergence of PZQ resistance, and to assist in the design of future treatment strategies.